Focal triggers initiating atrial fibrillation are thought to frequently arise from the pulmonary veins and their ostia. Surgeons have used the technique of modifying the substrate of the heart in these areas to prevent the propagation of the arrhythmia. In some patients with chronic atrial fibrillation, the Cos/MAZE III procedure has been employed. This procedure controls propagation of the depolarization wavefronts in the right and left atria by means of surgical incisions through the walls of the right and left atria. The incisions create blind or dead end conduction pathways, which prevent re-entrant atrial tachycardias from occurring.
While the Cox/MAZE procedure is successful is treating atrial fibrillation, the procedure is quite complex and is currently practiced by only a few very skilled cardiac surgeons in conjunction with other open-heart procedures. The procedure also is quite traumatic to the heart, as in essence, the right and left atria are cut into pieces and sewed back together, to define lines of lesion across which the depolarization wavefronts will not propagate. Still today, the Cox/MAZE procedure is done with traditional cut and sew techniques.
The market is demanding quicker, safer and less invasive approaches. As a result, there has been much recent research sod evaluation of mechanisms to encircle and isolate the pulmonary veins and replicate fee incisions of the MAZE operation. Companies are developing ablation techniques that heat (or cool) or chemically destroy the underlying tissue along these lines.
It has been suggested that procedures similar to the MAZE procedure could be instead, performed by means, of electrosurgical ablation, for example, by applying radio frequency energy to internal or external surfaces of the atria to create lesions across which the depolarization wavefronts will not propagate. Such procedures are disclosed in U.S. Pat. No 5,895,417, issued to Pomeranz, et ah (“the Pomeranz '417 patent”); U.S. Pat. No, 5,575,764 issued to Swartz., et al. (“the Swartz '766 patent”); U.S. Pat. No, 6,032,077, issued to Pomeranz (“the Pomeranz '077 patent”); U.S. Pat. No. 6,142,994, issued to Swanson, et at. (“the Swanson '994 patent”); and U.S. Pat. No. 5,871,523, issued to Fleischman, et al. (“the Fleischman '523 patent”), all incorporated herein by reference in their entireties.
The Pomeranz '417 patent discloses an apparatus for ablating tissue by making linear lesions within the chamber of a patient's heart by application of a plurality of spaced electrodes along an elongate member. The Schwartz '766 patent discloses a process for seating atrial arrhythmia, by creating discrete ablation tracks within both the left and right atrium. The Pomeranz '077 patent discloses an ablation catheter that is electrically connected to tissue to be ablated by a foam on the electrodes that is soaked in saline. The foam in the Pomeranz '077 patent acts as a conductive fluid to allow energy from the electrode to ablate the contacted tissue. The Swanson '994 patent discloses a surgical method and apparatus for positioning an element in the body of a patient for diagnosis or therapy. The apparatus in the Swanson '994 patent may be a catheter or a probe having a shaft with a lumen extending there through. The Fleischman '523 patent discloses a helically-wound emitter on an element with a insulating sheath movable over the emitter.
Various types of electrophyslology devices are used for ablating tissue. Typically, such devices include a conductive tip or blade that serves as one electrode In an electrical circuit that is completed via a grounding electrode coupled to the patient. The contact point is small or linear to create lesions to form linear tracks of ablated tissue. A power source creates high levels of electrical energy between the two electrodes causing the tissue to heat to a sufficient level to denature proteins within the tissue and cause cell death. In order for such procedures to be effective, if is desirable that the electrosurgically-created lesions are continuous along their length and extend completely through the tissue of the heart
Manufacturers have developed catheters that have a linear army of electrodes along a long axis (e.g., the Amazr, MECCA, and Revelation catheters). The surgeon positions the catheter and electrodes in contact with the tissue and either individually or sequentially applies energy to each electrode. Additionally, catheters that incorporate an electrode that is energized and moves along its length have been proposed, such as the Flex-10 from AFx. Inc., of 47929 Fremont Ave. Fremont, Calif. 94538.
Surgeons have also bees able to create linear lesions on the heart using applications of the same techniques. For example, Kottkamp, et. al. in an article entitled “Intraoperative Radio Frequency Ablation of Chronic Atrial Fibrillation: A Left Atrial Curative Approach by Elimination of Anatomic ‘Anchor’ Reentrant Circuits,” Journal of Cardiovascular Electrophysiology, 10:772-780 (1999), describe a hand-held device that creates as series of spot or short (less than 1 cm) linear lesions. Other investigators have used long, linear unipolar probes to create somewhat longer lesions. Still others have used multi-electrode linear catheters, similar to those described above to create a series of ablations that net a linear lesion.
The focus of most investigators has been to isolate the pulmonary veins. There is growing research that suggests this may not he necessary in the prevention and cure of atrial fibrillation, as discussed in the article by G. Stabile, P. Turco, V. La Rocca, F. Nocerino, E. Stabile, and A. De Simone entitled “Is Pulmonary Vein Isolation Necessary for Curing Atrial Fibrillation?,” Circulation, 108:657-660 (2003). Rather than focusing on only isolating the pulmonary veins, reduction in the overall volume of excitable tissue in the left atrium is sufficient to prevent atrial, fibrillation. The general concept is to ablate a large enough nonlinear area of the left atrium to prevent re-entrant waves and the propagation of atrial fibrillation.